The present invention relates in general to a gas exhaust system, and particularly, the present invention relates to an acoustical wind band for use with an exhaust device for exhausting gas from, for example, the interior of a building. The invention is especially useful in improving the entrainment of environmental air into the exhaust fume thereby improving the discharge velocity of the exhaust gas and therefore the effective stack height of the exhaust device and also in improving the sound attenuation of noise from the exhaust device or exhaust device outlet.
Conventional exhaust systems are typically manufactured having a fan and a nozzle device for pulling a gas out of the interior of a building and then increasing the velocity of the exiting air in order to properly dispel the air and also to avoid re-entrainment of the discharged air. In this regard, reference is made to U.S. Pat. No. 4,806,076, issued to Andrews, and U.S. Pat. No. 5,439,349, issued to Kupferberg, which are designed to provide a high velocity jet for exhausting atmosphere and other gases. These exhaust fans are typically mounted on the roof areas of buildings and are used to carry exhaust gases as high as possible above the roof line of the building so as to ensure an effective final dilution of the gases within the greatest possible volume of ambient air and to ensure their dispersal over a large area with maximum dilution.
For example, the radial upblast exhaust fan apparatus described and shown in U.S. Pat. No. 4,806,076 has a nozzle in which two converging flow paths are defined by two respective passageways. A fan means is positioned within the fan housing to urge exhaust gases to flow upwardly through the exhaust paths. A passive zone located between the two flow paths supplies environmental air for mixing by induction into the contaminated gases being exhausted through the converging flow paths.
In addition, prior art devices for exhausting gases to atmosphere can have a wind band, or annular ring, that may be positioned vertically extending in general parallel relationship with respect to an upper end of the fan or nozzle housing in order to facilitate mixing of the exhausted gas with ambient environmental air. For example, a wind band can be provided at one end of the two passages at the outlets of the radial upblast exhaust fan apparatus described and shown in U.S. Pat. No. 4,806,076, to provide an entrainment of fresh air to mix with and dilute the gases exhausting from the two passageways. Another conventional wind band is shown and described in U.S. Pat. No. 5,439,349, which describes a ring defining an annulus provided at the outlet end of a bifurcated stack to induce ambient air to mix with the spent air exhausting from the bifurcated tubular member.
Typically, the wind band is located in spaced relation with respect to an outer wall of the fan or nozzle housing by, for example, a wind band bracket means. In this manner, when gases are exhausted through the discharge of the exhausting device, ambient environmental air will be introduced between the space, formed between the outer wall of the exhausting device and the side wall of the wind band, and mix with and dilute the exhausting gases. However, conventional wind bands are limited in the amount of entrainment that they can achieve due to their design and construction.
In addition, conventional exhaust fans for moving large volumes of air often generate high levels of noise which is undesirable. As a result, a wide variety of fan silencing equipment has been proposed to absorb fan noise, thereby reducing fan noise to an acceptable level. However, conventional silencers are typically used at the fan portion of the device, and thus do not control noise at the nozzle or outlet portion. These conventional silencers are undesirable for several reasons, including because they lead to an increase in the overall height of the fan device and they are limited to a relatively low air distribution velocity (on the order of less than about 3000 feet per minute) in which they are effective (e.g., provide maximum attenuation without themselves generating any significant additional noise).
One conventional exhaust system that attempts to reduce fan noise at the nozzle or outlet portion to an acceptable level is pending U.S. patent application entitled xe2x80x9cAcoustic Silencer Nozzlexe2x80x9d, Ser. No. 09/390,796, filed Sep. 7, 1999, which describes a high velocity silencer nozzle for reducing the amount of noise generated by the exhausting gases as they exit through the exhausting device. The acoustic silencer nozzle provides acoustically absorbing media or resonating chambers adjacent the converging exhaust paths of the nozzle. In this manner, the noise at the nozzle or outlet portion is reduced and a tighter plume of high discharge flow is achieved. However, these conventional silencers are limited in their ability to block noise, such as line of sight noise, from the exhausting gas at the outlet portion or portions of the exhaust device.
Therefore, a need exists for a device that improves the entrainment of ambient environmental air with the exhausting gases and also that improves sound attenuation of the discharging gases at the outlet portion of the fan, nozzle, stack, silencer, ducting, or the like, while still maintaining a relatively low height of the exhausting device and providing a relatively high air distribution velocity, without adding significantly to system pressure.
The present invention is directed to an apparatus, system, and method for improving the entrainment of ambient environmental air with the exhaust gas passing through the acoustical wind band and for improving the attenuation of sound from the exhaust gas exiting the exhaust device. The acoustic wind band apparatus can be used with a gas exhaust device having a discharge outlet portion for exhausting gas in a gas exhaust system. The acoustical wind band includes a plurality of spaced apart wind band sections, each wind band section having a top end defining a top opening, a bottom end defining a bottom opening, and one or more side walls disposed between and connecting the top end to the bottom end. The plurality of wind band sections are disposed circumferentially and in vertical spaced relation over the discharge outlet portion of the gas exhaust device and extending generally upward therefrom.
The acoustic wind band apparatus includes a plurality of passages formed around a peripheral of the acoustical wind band and disposed circumferentially about the discharge outlet portion. Each passage draws a flow of gas from environmental atmosphere outside the acoustical wind band to induce a flow of environmental gas from therebelow to mix with and dilute gas from the discharge outlet portion inside the acoustical wind band. The number of the plurality of passages corresponds to a number of the plurality of wind band sections. The acoustic wind band includes at least a first passage formed between one of a top wall and a side wall of the exhaust device and the side wall of the lower most wind band section and at least a second passage formed between a second wind band section side wall and the first wind band side wall.
Each sections can include one of a cylindrical shape, a straight conical shape, a curved conical shape, a square shape, and a rectangular shape. The bottom opening and the top opening can comprise one of a circular shape, a square shape, and a rectangular shape. Preferably, the side walls of adjacent sections of the plurality of wind band sections are parallel with respect to one another. Each wind band section has a smallest diameter or width greater than a diameter or width of the discharge outlet portion.
Preferably, the first, lowest most, wind band section is positioned over and about the discharge portion and each vertically successive section is larger than the preceding section and each vertically successive section is positioned over and about the preceding section. Alternatively, the first, lowest most, wind band section can be positioned over and about the discharge portion and each vertically successive section can be smaller than the preceding section and each vertically successive section can be positioned over and within the preceding section.
The acoustic wind band apparatus includes support structures disposed between and connection the acoustical wind band to the exhaust device. The support structures also hold the plurality of wind band sections in spaced apart relation with respect to one another.
The acoustical wind band can be constructed to improve sound attenuation of the exhaust gas exiting the exhaust device. For example, the bottom end of the first, lowest most, wind band section preferably extends at least to a horizontal plane defined by a line of sight of the discharge outlet portion and the bottom end each vertically successive wind band section preferably extends at least to a horizontal plane defined by the top end of a vertically preceding wind band section.
A further embodiment within the scope of the present invention is directed to a system that improves the entrainment of ambient environmental air with the exhausting gases and also that improves sound attenuation of noise generated by the exhaust device or by the discharging gases at the outlet portion of the device. The system includes an exhaust device and an acoustical wind band. The exhaust device can include any conventional exhaust device, including for example, a fan, a nozzle, a stack, a silencer, ducting, piping, or the like. A gas movement device is provided as part of, or separately from the gas exhaust device. A drive mechanism, such as an electric motor, is provided to generate a flow of exhaust gas through the exhaust device. The drive mechanism can be directly coupled to the gas movement device, or may be indirectly coupled to the gas movement device through, for example mechanical linkage or belt and pulley arrangement.
In one embodiment of the present invention, the exhaust device can include a radial upblast, mixed flow, centrifugal, or axial exhaust fan, including a main housing having a fan housing in the lower section thereof and acoustic silencer nozzle positioned above the fan housing and extending upwardly therefrom. The exhaust device can include one or more vertical flow paths and thus one or more upper contaminated air outlets.
In another embodiment of the present invention, the exhaust device can include an exhaust fan apparatus, such as a centrifugal fan scrolling casing, with a centrifugal fan impeller mounted on an axle within the casing and having an axis of rotation at right angels to the side members of the scroll casing. In operation, the impeller, driven by motor, draws an exhaust gases from a building containing airborne contaminants through duct and then upwardly into the stack or nozzle by first passing through a diffuser and then double passageways.
The acoustical wind band apparatus is positioned circumferentially around and in vertical spaced relation over the discharge outlet portion of the gas exhaust device and extending generally upward therefrom. The acoustical wind band includes a plurality of passages formed around a peripheral of the acoustical wind band and disposed circumferentially about the discharge outlet portion. Each passage draws a flow of gas from environmental atmosphere outside the acoustical wind band to induce a flow of environmental gas from therebelow to mix with and dilute gas from the discharge outlet portion inside the acoustical wind band. A flow of fluid exiting one or more exhaust flow paths and passing through the acoustical wind band sets up aspiration in such a manner so that the further flow of fluid is drawn from ambient atmosphere through the passages. The acoustical wind band can be constructed to improve sound attenuation by blocking a direct line of sight of noise generated to the exhausting gas. Preferably, a bottom end of a first, lowest most, wind band section extends at least to a horizontal plane defined by a line of sight of the discharge outlet portion and the bottom end each vertically successive wind band section extends at least to a horizontal plane defined by a top end of a vertically preceding wind band section.
A further embodiment within the scope of the present invention is directed to a method for improving the entrainment of ambient environmental air with the exhausting gases, while still maintaining a relatively low height of the exhausting device, thus providing a relatively high air distribution velocity, without adding significantly to system pressure. The method includes providing a gas exhaust device having a gas inlet opening for receiving a gas to be exhausted and a gas outlet opening for discharging the gas to atmosphere, disposing an acoustic wind band having a plurality of vertically spaced apart wind band sections over and about the exhaust gas outlet of the exhaust device, forming a plurality of passages for drawing ambient environmental air from a point outside the acoustical wind band to a point inside the acoustical wind band, wherein a number of the plurality of passages corresponds to a number of the plurality of wind band sections, and wherein a first passage is formed between a housing of the gas exhaust device and an inner surface of the lower wind band section and each successive passage is formed between an outer surface of a preceding wind band section and an inner surface of a successive wind band section, and inducing a plurality of flows of ambient environmental air through the plurality of passages to be mixed with and dilute the exhaust gas discharging from the exhaust device discharge.
According to another aspect of the invention, the method includes forming each of the wind band sections extending upward and inward to form an angle inclined toward an upper, center region of the acoustical wind band. The angles act to increase one or more of a velocity and a volume of the exhaust gas flowing through the acoustical wind band.
A further embodiment within the scope of the present invention is directed to a method for improving sound attenuation in a gas exhaust system, such as a fan, nozzle, stack, silencer, ducting, piping, or the like. The method includes providing a gas exhaust device having a gas inlet opening for receiving a gas to be exhausted and a gas outlet opening for discharging the gas to atmosphere, disposing an acoustic wind band having a plurality of vertically spaced apart wind band sections over and about the exhaust gas outlet of the exhaust device, positioning a first, lower wind band section such that at least a portion of a bottom end of the lower wind band section blocks a direct line of sight from a point outside the exhaust device and the lower wind band section from a point inside the exhaust device and the lower wind band section, positioning each vertically successive wind band section such that at least a portion of a bottom end of a vertically successive wind band section blocks a direct line of sight from a point outside a vertically preceding wind band section and the successive wind band section from a point inside the preceding wind band section and the successive wind band section, and blocking noise generated by the exhaust device and the exhaust gas outlet opening from radiating along a direct line of sight from a point inside the acoustical wind band and the exhaust device to a point outside the acoustical wind band and the exhaust device.
According to another aspect of the invention, the method includes forming each of the wind band sections extending upward and inward to form an angle inclined toward an upper, center region of the acoustical wind band. The angles act to reflect noise inward and upward through the acoustical wind band thereby improving sound attention.